Bacteria Cell Wall

10 Key excerpts on "Bacteria Cell Wall"

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  Cell Technology

  • Khushboo Chaudhary(Author)
  • 2023(Publication Date)
  • Delve Publishing

    (Publisher)

  “A cell wall is a structural layer surrounding some types of cells, just outside the cell membrane. It can be tough, flexible, and sometimes rigid. It provides the cell with both structural support and protection, and also acts as a filtering mechanism”. Cell Technology 24 Figure 1.9: Gram-positive and gram-negative. Bacterial Cell Wall Peptidoglycan is a huge polymer of interlocking chains of alternating monomers. It provides a rigid support while freely permeable to solutes. The backbone of the peptidoglycan molecule is composed of two amino sugar derivatives of glucose. The “glycan” part of peptidoglycan. • N-acetylglucosamine (NAG) • N-acetlymuramic acid (NAM) NAG / NAM strands are connected by interlocking peptide bridges. The “peptide” part of peptidoglycan is shown in figure 1.10. “The bacterial cell wall consists of peptidoglycan, an essential protective barrier for bacterial cells that encapsulates the cytoplasmic membrane of both Gram-positive and Gram-negative bacterial cells. Peptidoglycan is a rigid, highly conserved, complex structure of polymeric carbohydrates and amino acids”. Cell Biology 25 Figure 1.10: Prokaryotes - Cell Wall. Prokaryotes – Glycocalyx Some bacteria have an additional layer outside of the cell wall called the glycocalyx. This additional layer can come in one of two forms: 1. Slime Layer Glycoproteins loosely associated with the cell wall. Slime layer causes bacteria to adhere to solid surfaces and helps prevent the cell from drying out. The slime layer of Gram+ Streptococcus mutans allows it to accumulate on tooth enamel (yuck mouth and one of the causes of cavities). Other bacteria in the mouth become trapped in the slime and form a biofilm & eventually a buildup of plaque. 2. Capsule Polysaccharides are firmly attached to the cell wall. The capsules adhere to solid surfaces and to nutrients in the environment. The adhesive power of capsules is a major factor in the initiation of some bacterial diseases.

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  Veterinary Microbiology and Microbial Disease

  • P. J. Quinn, B. K. Markey, F. C. Leonard, P. Hartigan, S. Fanning, E. S. Fitzpatrick(Authors)
  • 2011(Publication Date)
  • Wiley-Blackwell

    (Publisher)

  Section II Introductory Bacteriology Passage contains an image Chapter 7 The structure of bacterial cells

  A typical bacterial cell is composed of a capsule, a cell wall, a cell membrane, cytoplasm containing nuclear material and appendages such as flagella and pili (fimbriae). Certain species of bacteria can produce forms termed endospores or spores, which are resistant to environmental influences. Some of the structural features of pathogenic bacteria which are important in the production of disease or may be useful for the laboratory diagnosis of infection are reviewed in Chapters 10 and 13. The principal structural components of bacterial cells are presented in Table 7.1 and illustrated in Fig. 7.1 .

  Capsule

  Bacteria can synthesize extracellular polymeric material which is usually described as glycocalyx. In some bacterial species this polymeric material forms a capsule, a well defined structure closely adherent to the cell wall. A slime layer is formed when the polymeric material is present as a loose meshwork of fibrils around the cell. Most capsules are composed of polysaccharides; Bacillus species such as B. anthracis produce polypeptide capsules. Defined capsules can be visualized by light microscopy using negative staining techniques. Bacteria with well defined capsular material produce mucoid colonies on agar media. However, the capsules of most species of bacteria can be demonstrated only by electron microscopy or by immunological methods using antisera specific for the capsular (K) antigens. The main function of capsular material appears to be protection of the bacterium from adverse environmental conditions such as desiccation. In the body, capsules of pathogenic bacteria may facilitate adherence to surfaces and interfere with phagocytosis.

  Cell wall

  The tough, rigid cell walls of bacteria protect them from mechanical damage and osmotic lysis. As cell walls are non-selectively permeable, they exclude only very large molecules. Differences in the structure and chemical composition of the cell walls of bacterial species account for variation in their pathogenicity and influence other characteristics including staining properties. Peptidoglycan, a polymer unique to prokaryotic cells, imparts rigidity to the cell wall. This polymer is composed of chains of alternating subunits of N -acetylglucosamine and N

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  Microbiology and Nanobiology: Advancing Frontiers

  • Kumar, Har Darshan(Authors)
  • 2021(Publication Date)
  • Daya Publishing House

    (Publisher)

  Chapter 5 Microbial Morphology and Physiology Bacterial Cell Walls and Surface Structures Some of the most important structures of microbial cells are their surfaces. The surfaces are in immediate contact with the external environment. The cell walls admit nutrients and release wastes, and yet need to resist internal turgor pressure and environmental insults so as to maintain cellular shape. Walls facilitate adherence of cells to other surfaces and provide space for specialized structures such as flagella, pili, spines, capsules, S-layers, and exopolymeric substances (EPS) (Beveridge, 2006). Exploring the native architecture of bacterial surfaces has traditionally relied on electron microscopy, which uses high vacuum and high voltages. This imposes the limitation that only dry specimens can be imaged, yet living cells and their structures strongly depend on water and its ability to interact with and configure molecular ingredients. Advances in cryo-transmission electron microscopy (cryoTEM) are overcoming this problem by allowing researchers to examine native, hydrated structures in bacteria and their associated biofilms. Early preparations made by using TEM (transmission electron microscopy) 4-5 decades ago, revealed a centrally condensed, nonenveloped chromosome surrounded by randomly distributed ribosomes and highlighting concept of an anucleate ( i.e. , prokaryotic) cell. These images also revealed a basic difference between gram-positive and gram-negative bacteria, which have more complex walls consisting of an outer membrane, a thin This ebook is exclusively for this university only. Cannot be resold/distributed. peptidoglycan layer, and a periplasmic space filled with periplasm. Gram-positive walls are sometimes 20-fold thicker than the peptidoglycan in gram-neative bacteria and usually contain secondary polymers, such as teichoic and teichuronic acids, attached to a peptidoglycan network. Removal of water shrinks most structures and reshapes macromolecules.

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  An Introduction to Microbiology

  Pharmaceutical Monographs

  • W. B. Hugo, J. B. Stenlake(Authors)
  • 2014(Publication Date)
  • Butterworth-Heinemann

    (Publisher)

  A photograph of such a cell wall preparation of Staphylococcus aureus taken with an electron microscope is shown in Fig. 4. Wall structure varies considerably between bacterial species and these structures play important roles both in determining the fundamental properties of the organism and in determining their response to drug action. 4 TERMINAL ORGAN OF FLAGELLUM 10-20 nm GRANULES RIBOSOMES illllllllll~1111111111 SLIME 600 nm ,/ GRANULES ........ VOLUTIN GRANULES NUCLEAR MATERIAL POLAR FLAGELLUM ....... •. THE BACTERIAL CELL FIG. 4. Cells of Staphylococcus aureus disintegrated by shaking with small glass beads. One cell in the group has remained intact. (Thanks are due to Dr A. S. McFarlane and the editor of the British Medical Journal for per-mission to publish and Burroughs Wellcome and Co. for providing the original photograph) Before 1948 very little was known of the chemical structure of the bacterial cell wall but since then a large literature has accumulated. A fundamental structure found in the cell walls of all bacteria and the blue-green algae i.e. procaryotic cells (page 118) has been called mucopeptide, murein, glycosaminopeptide, glycopeptide, peptidoglycan or the murein sacculus. Peptidoglycan is the pre-ferred term. The first hint as to the nature of this component came in 1952 when Park, while studying the action of penicillin on staphylo-cocci, noted the accumulation of a complex nucleotide which con-tained what was later to be confirmed as a component of the cell wall. As stated above it was known that, like other cells, a strong or rigid component must be present in bacterial cell walls to with-stand the osmotic pressure exerted by the cytoplasmic contents of the cell and also to confer the characteristic shape of sphere or rod.

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  Medical Microbiology and Infection

  • Tom Elliott, Anna Casey, Peter A. Lambert, Jonathan Sandoe(Authors)
  • 2012(Publication Date)
  • Wiley-Blackwell

    (Publisher)

  The cell wall is important in protecting bacteria against external osmotic pressure. Bacteria with damaged cell walls, e.g. after exposure to β-lactam antibiotics such as penicillin, often rupture. However, in an osmotically balanced medium, bacteria deficient in cell walls may survive in a spherical form called protoplasts. Under certain conditions some protoplasts can multiply and are referred to as L-forms. Some bacteria, e.g. mycoplasmas, have no cell wall at any stage in their life cycle.

  The cell wall is involved in bacterial division. After the nuclear material has replicated and separated, a cell wall (septum) forms at the equator of the parent cell. The septum grows in, produces a cross-wall and eventually the daughter cells may separate. In many species the cells can remain attached, forming groups, e.g. staphylococci form clusters and streptococci form long chains (Figure 1.5 ).

  Figure 1.5 Some groups of bacteria.

  Capsules

  Some bacteria have capsules external to their cell walls (Figure 1.3 ). These structures are bound to the bacterial cell and have a clearly defined boundary. They are usually polysaccharides with characteristic compositions that can be used to distinguish between microorganisms of the same species (e.g. in serotyping). Capsular antigens can be used to differentiate between strains of the same bacterial species, e.g. in the typing of Streptococcus pneumoniae for epidemiological purposes. The capsules are important virulence determinants in both Gram-positive and Gram-negative bacteria, because they may protect the bacteria from host defences and, in some bacteria, aid attachment to host cells.

  Bacterial Slime and Biofilm

  Extracellular slime layers are produced by some bacteria. They are more loosely bound to the cell surface than capsules and do not form a clearly defined surface boundary. The slime layer is composed predominantly of complex polysaccharides (glycocalyx), which acts as a virulence factor through the formation of biofilm, e.g. by facilitating the attachment of Staphylococcus epidermidis onto artificial surfaces, such as intravascular cannulae (Figure 1.6

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  Biochemistry and Physiology of Bifidobacteria

  • Anatoly Bezkorovainy(Author)
  • 2020(Publication Date)
  • CRC Press

    (Publisher)

  Chapter 5

  STRUCTURAL COMPONENTS OF BIFIDOBACTERIA

  Anatoly Bezkorovainy

  TABLE OF CONTENTS

  I.  Cell Wall Structure A.  Introduction B.  Composition of Bifidobacterial Cell Walls C.  Peptidoglycan (Murein) Structures D.  Biosynthesis of Peptidoglycans E.  Polysaccharide Component of the Cell Wall F.  Teichoic Acid-Like Substances II.  Protoplast Formation and Membrane Properties III.  Circulating Antibodies to Bifidobacteria IV.  Summary References

  I. CELL WALL STRUCTURE

  A. Introduction

  Bacterial envelopes consist of a number of structures of varying complexity, including membranes and cell walls of different types. These structures maintain cell shape and protect the bacteria against osmotic shock. The envelopes of Gram-negative bacteria consist of three layers: the outer membrane, the peptidoglycan (murein) layer, and the plasma membrane. The outer two layers are referred to as the cell wall.1 The outer membrane is connected to the peptidoglycan layer by a lipoprotein anchor, and the space between the two layers is referred to as the periplasmic space. The outer membrane consists of lipopolysaccharide, lipoprotein, and phospholipids. The lipopoly saccharide is on the outer surface of the outer membrane, whereas the phospholipid is on the inner surface.2 The peptidoglycan layer may be monomolecular, with the carbohydrate portion (N-acetylmuramic acid-N-acetylglucosamine polymer) facing the outer membrane and the amino acid residues facing the plasma membrane. The Escherichia coli peptidoglycan has the following structure:3

  where MurNAc is N-acetylmuramic acid, GlcNAc is N-acetylglucosamine, and meso-DAP is meso-diaminopimelic acid.

  The cell wall of Gram-positive microorganisms is much simpler than that of the Gram-negative ones. It is a single structure consisting of three macromolecular components: polysaccharide, peptidoglycan (murein), and lipoteichoic acid. The latter, which may account for as much as 30 to 50% of the cell wall mass, is anchored to the plasma membrane via its fatty acyl hydrocarbon chains, whereas the polar glycero (or ribitol) phosphate residues penetrate the peptidoglycan layer.2 Teichoic acids are either glycerol or ribitol phosphate polymers (usually 1,3- or 1,5-phosphodiester linkages, respectively), where the terminal glycerol residue -OH groups may be esterified with fatty acids. A typical teichoic acid from Staphylococcus aureus is shown below:4

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  Bacterial Cell Wall

  • J.-M. Ghuysen, R. Hakenbeck(Authors)
  • 1994(Publication Date)
  • Elsevier Science

    (Publisher)

  I -M Gl~uyscn and R I lakenbeck (Eds ), Hocrertd (‘d Wd 0 1994 Elsevier Science B V. All rights reserved 23 CHAPTER 2 Bacterial peptidoglycan: overview and evolving concepts HARALD LABISCHINSKI and HEINRICH MAIDHOF Robert Koch-Institute of the Federal llealth Office. Nordufer 20, 0-13353 Berlin 65, Germany 1. Introduction The essential cell wall polymer of most eubacteria, peptidoglycan (synonym: murein), has attracted and fascinated scientists from many different disciplines since its distinct chemi- cal composition and its unique role as an ‘exoskeleton’ were discovered more than 30 years ago (Chapter I ) . Within a relatively short time, the basic chemical structure of this large, bag-like molecule (also called the sacculus, see Fig. 1) was elucidated, giving access to an increasingly refined knowledge of its spatial and morphological arrangement. Because the mode of action of the most important group of antibacterial drugs, the B-lac- tam antibiotics, and the mechanisms that the bacteria have developed to survive in the presence of these antibiotics, are related to the biosynthesis, three-dimensional structure and morphogenesis of the peptidoglycan, even more efforts have been undertaken to gain a detailed knowledge of the chemistry and structural features of the murein network.

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  Structure

  • I.C. Gunsalus(Author)
  • 1960(Publication Date)
  • Academic Press

    (Publisher)

  Under the experimental conditions used, the weight of bacterial wall material may increase from 50 to 100% while the inhibition of uptake of amino acids into the cellular protein fraction may be from 85 to 98 %. 131 · 27 ° The use of chloramphenicol therefore provides a suitable experimental system for the study of certain cell wall syntheses in the absence of protein syn-thesis. H. FUNCTIONS OF THE CELL WALL There is little doubt that the mechanical protection afforded by the rigid bacterial wall confers upon those organisms possessing such structures a considerable survival advantage over those species devoid of a wall. It is evident from the studies with bacterial protoplasts 271 · 272 that the soft struc-tures underlying the rigid outer wall require rather special conditions for the maintenance of their integrity; without these conditions the protoplast, deprived of its protective cell wall, would have a precarious and ephemeral existence. The bacterial wall must possess sufficient mechanical strength to with-stand the high pressures that can be exerted by the intracellular solutes. Mitchell and Moyle 273 have found that the solute concentration in £. aureus may exert an osmotic pressure equivalent to 20 atmospheres. It is therefore understandable that any serious defect in the mechanical conti-nuity of the wall will lead to a rupture of the weaker underlying protoplast SURFACE LAYERS OF THE BACTERIAL CELL 143 membrane; ultimately the organisms will lyse and die. Impairment of the mechanical strength of the wall by penicillin action thus frequently culmi-nates in lysis. Many halophilic bacteria obviously possess walls unable to withstand the pressures exerted upon them when the external environment is diluted. 15 Although the bacterial cell wall affords such great survival value, it is by no means indispensable for the biological and biochemical continuity of the cell.

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  Structure and Ultrastructure of Microorganisms

  An Introduction to a Comparative Substructural Anatomy of Cellular Organization

  • E. M. Brieger(Author)
  • 2013(Publication Date)
  • Academic Press

    (Publisher)

  In this field as in so many others the cell wall has up till now benefited more from chemical and immuno-chemical methods than from the study of its macromolecular organization as revealed by the electron microscope. In fact we would know nothing about the complexity of the cell wall organization if we had to rely solely on electron microscopical evidence. In the cell walls of Pseudomonas fluorescens, Rhodopseudomonas sphéroïdes, and E.coli, and B.megaterium, Salton and Williams (1954) did not find any evidence of macromolecular organization. In Rhodospirillum rubrum it seems probable that the macromolecules of the cell wall are protein in nature, but the fine structure of the cell wall did not change after treatment with trypsin. Yet although the macromolecular structure and the chemical constituents of bacterial cell walls differ from that seen in the cellulose walls of plants, there is no reason to assume that the mechanism of growth, maintenance and reconstitution is different. III. T H E B A C T E R I A L C E L L W A L L I N T H I N S E C T I O N S Not much attention has been given to the study of the structure of the bacterial cell wall in electron micrographs of thin sections. Only since the introduction of lanthanum nitrate and uranyl acetate as electron stains III. T H E B A C T E R I A L C E L L W A L L I N Τ Η Γ Ν S E C T I O N S 267 has it been possible to analyze its structure further. Kellenberger and Ryter (1958), in their study on the integument system of E. coli, expressed the view that the cell wall in this, and possibly other Gram-negative organisms, is composed of several layers, with the cytoplasmic membrane fitted to the inner layer. In sections it is seen as a dense band bounded on either side by a sharply defined dense line of 20-30 À width.

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  Bacterial Physiology

  • C. H. Werkman, P. W. Wilson, C. H. Werkman, P. W. Wilson(Authors)
  • 2013(Publication Date)
  • Academic Press

    (Publisher)

  However, under reasonably standardized conditions the type of inclusions produced by an organism is a character as stable as most of the physiological characters used in taxonomy. It may be used to characterize a group such as the formation of sulfur or iogen inclusions, or a species as was done by Arthur Meyer (1912) in the genus Bacillus. F. THE CELL WALL The cytoplasm and cytoplasmic membrane occupy a cavity limited by the cell wall. The cell Avail is a very thin membrane endowed with a variable degree of rigidity, ductility, and elasticity. When the cell is plasmolyzed, the cell wall is sufficiently rigid to hold its form unsup- ported by the shrunken protoplasm; the so-called "ghost cells" consist of the cell wall, with or without the cytoplasmic membrane or remnants of it, after the protoplasm disappears by autolysis. On the other hand, rigidity of the cell wall is not of a high order, and it collapses vertically to a variable extent when the protoplasm is of a low solid content (Fig. 2.8), and undergoes considerable shrinkage upon drying. Ductility of the cell wall is concluded from instances of extreme stretchability observed in electron micrographs. Its elasticity may also be concluded from various considerations, but it was directly demonstrated by microdis- section (Wâmoscher, 1930). The cell wall possesses also a variable degree of stickiness, an extreme case of which was observed in an avian s train of Mycobacterium tuberculosis. THE STRUCTURE OF THE BACTERIAL CELL 45 The cell wall has a low réfringence and is not visible when normal cells are observed in dark field; the bright line which surrounds the cells in dark field corresponds to the cytoplasmic membrane (Fig. 2.9); "ghost cells" are barely visible in dark field, and the slight réfringence they show is partly due to remnants of the cytoplasmic membrane. The FIG. 2.9. Strain C3 of Bacillus cereus. A dark-field photomicrograph of two actively growing cells.

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